Pacemakers and other implantable devices such as cardiac defibrillators require a method of passing electrical signals between the device and the heart. To transmit these signals from the device to the heart, implantable electrical leads are used. The leads make electrical contact with the device through the connector top ring and tip contacts. The signals are then transmitted from the device to the heart via the implantable leads. To ensure an uninterrupted electrical path between the device and the heart, a strong reliable mating between the implantable leads and the connector top of the device is necessary. It is also desirable to seal the entrance of the connector top of the device from body fluids. To achieve these connector conditions, external calibrated torque wrenches are used to secure the leads in place by means of set screws or by compressing an active seal. The use of external tools for achieving connector conditions has created reliability problems (cored septum, stripped wrench, hex, and the like). Further, time is required to insure electrical contact while the tool is being used.
Modern pacemakers monitor the activity of a heart and provide a stimulation pulse in the absence of normal heart activity. Advantageously, such devices are relatively small, light-weight and implantable. In order to sense and stimulate the heart, however, such pacemakers must be used with a pacemaker lead--an electrical conductor that carries electrical signals between the heart and the pacemaker. Advantageously, the pacemaker lead can be inserted into the heart transvenously through a relatively simple and well-known surgical procedure. Disadvantageously, one end of the lead (designated herein as the "connecting end") must be electrically and mechanically secured to the pacemaker in a way that provides for a long-term safe and secure, yet detachable, connection. Those skilled in the pacemaker art have long sought for a simple, yet reliable and safe, means for making this detachable electrical and mechanical connection between the pacemaker device and the connecting end of the pacemaker lead.
In order to appreciate the advantages of the present invention, it will help first to have a basic understanding of the manner in which the mechanical and electrical connection functions are carried out in prior art pacemakers. The main components associated with the connection function of known prior art pacemakers are shown in FIGS. 1 and 2. A pacemaker 10 electrically includes a battery 14 that powers electrical circuits 12. The pacemaker electrical circuits 12 and battery 14 are mechanically housed and hermetically sealed in a suitable housing 16. Typically, this housing or case 16 is shaped to include a flat side or platform 20 to which a suitable epoxy connector 22 can be bonded. At least one feed through terminal 18, in electrical contact with the electrical circuits 12, passes through the case or housing 16 and protrudes out from the platform 20. This feed through terminal 18 is electrically isolated from the case 16. A platinum wire 24, or other suitable conductive element, connects the terminal 18 to a conductive connector block 26 that is fitted within the connector 22. A pacemaker lead 28, having a proximal electrode 30, connects to the pacemaker electrical circuits by inserting the proximal electrode 30 into a receiving channel 31 of the connector 22 until the electrode 30 is in contact with the connector block 26. A set screw 32 is then securely tightened using a torque wrench 34 to firmly hold the electrode 30 in both mechanical and electrical connection with the connector block 26. A septum (not shown) is typically placed over the set screw 32 in order to prevent body fluids from seeping through the set screw hole. Further, sealing ribs or rings 36 on the connecting end of the pacemaker lead are designed to tightly engage the inside edges of the receiving channel 31 in order to prevent any body fluids from entering into the receiving channel 31 once the connecting end of the lead has been pushed into the connector 22.
Representative descriptions of many of the features and functions of prior art pacemaker connection systems may be found in U.S. Pat. Nos. 5,433,734 and 5,324,312 to Stokes et al.; U.S. Pat. No. 4,942,876 to Gotthardt; U.S. Pat. No. 4,934,366 to Truex et al.; U.S. Pat. No. 4,932,409 to Hirschberg; and U.S. Pat. No. 4,259,962 to Peers-Trevarton. Most notable of these, for purposes of the present invention, is the patent to Truex et al., in which a feedthrough connector for an implantable medical device combines the connector function with the feedthrough function and eliminates the need for the cast epoxy connector previously used on such devices. The feedthrough connector includes a barrel assembly having open and closed ends. The open end of the assembly has an opening for receiving a slidably inserted electrical lead. The barrel assembly includes cylindrical metal, conductive portions separated by cylindrical ceramic insulating portions. Spring contacts are mounted on the inside of the metal portions and are adapted to make mechanical and electrical contact with the appropriate contacts of an electrical lead when the lead is inserted into the connector. The outer side of the metal portions are electrically connected to the appropriate electrical circuit within the housing, and the open end of the barrel assembly is welded to the device housing so that the inside of the device can be hermetically sealed. Releasable lead gripping means are included as part of the barrel assembly to detachably lock and seal the electrical lead in its inserted position inside of the connector.
While that which is described in these prior patents varies greatly relative to, for example, different types of locking mechanisms for performing the mechanical connection function, or different types of arrangements for performing the electrical feedthrough function, including the use of bipolar or multiple connector leads, all such systems include the use of a premolded or cast connector 22 that is bonded to a sealed pacemaker housing 16 in which the electrical circuits are located.
Typically, known connectors 22 are cast in place from epoxy to the platform or header 20 of the pacemaker, or a premolded connector is bonded to the platform 20 using a suitable sealing and bonding agent. Further, once the electrical connection is made from the terminal post 18 to the connector block 26, and the connector is attached to the housing, all remaining voids within the connector 22, not including the receiving channel 31 into which the proximal end of the lead is to be inserted, must be filled with a suitable filler material, such as a two-component epoxy or silicone rubber.
It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.